Japanese Patent Application Laid-open No. 2012-26564 describes one conventional example of a hydraulic shock absorber which includes, inside a cylindrical damper case: a cylinder which demarcates a piston oil chamber and a rod oil chamber so as to sandwich a piston; an outer cylinder body which is arranged outside the cylinder, which demarcates between the cylinder and the outer cylinder body a reflux path that connects the piston oil chamber and the rod oil chamber with each other, and which demarcates between the damper case and the outer cylinder body a reservoir chamber that compensates for oil corresponding to tension and compression of a piston rod; and a valve structure which is mounted to each open end of the cylinder and the outer cylinder body on the side of the piston oil chamber and which is provided with a valve for controlling a flow of oil between the piston oil chamber and the reflux path and between the piston oil chamber and the reservoir chamber.
The valve structure described in Japanese Patent Application Laid-open No. 2012-26564 is constituted by a first base piston and a second base piston, and the base pistons are overlaid on each other and integrated by a bolt. The respective open ends of the cylinder (an inner cylinder described in Japanese Patent Application Laid-open No. 2012-26564) and the outer cylinder body (an outer cylinder described in Japanese Patent Application Laid-open No. 2012-26564) are both fixed to the integrated base pistons by press-fitting.
With a structure in which a cylinder and an outer cylinder body are concentrically mounted to a valve structure as is the case with the hydraulic shock absorber described in Japanese Patent Application Laid-open No. 2012-26564, if the outer cylinder body is first press-fitted into the valve structure, the degree of press-fitting of a press-fit portion of the subsequent cylinder cannot be visually observed. Therefore, when mounting the cylinder and the outer cylinder body to the valve structure, two press-fitting steps are conceivably adopted in which the inner cylinder is first press-fitted and the outer cylinder body is subsequently press-fitted. However, since the cylinder and the outer cylinder body are elongated parts, there is a problem with an operation of further overlaying the outer cylinder body from the outside to the valve structure to which the cylinder has already been mounted in that handling of the parts is troublesome and work efficiency is likely to decline.
A specialized jig can conceivably be used to press-fit the cylinder and the outer cylinder body at the same time. However, in this case, since a press-fit portion of the cylinder cannot be visually observed as described earlier, a need arises to use a dedicated assembly machine with high press-fitting management accuracy.